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The European Space Agency (ESA) began monitoring sea-surface temperature in 1991 with the first Along-Track Scanning Radiometer instrument on the ERS-1 satellite (shown here), followed by instruments on ERS-2 and Envisat. ESA will continue observing sea-surface temperature with the upcoming Sentinel-3 mission.

Global satellite data show a 30-year uptrend of sea-surface temperature has slowed during the last 15 years—not the end of global warming, but a shuffle in the climate system’s energy flow.

Like flying thermometers, some satellites carry instruments that provide a global view of the surface temperature of oceans and seas. Measuring the sea-surface temperature is important for improving weather and ocean forecasting and climate change research.

Satellite and local readings show that sea-surface temperature has been rising rapidly since the 1970s in line with the overall warming of our planet. But this increase has slowed significantly during the last 15 years. In contrast, other variables, such as increasing atmospheric carbon dioxide, rising sea levels and declining Arctic sea ice, haven’t experienced the same reduction trend and therefore demonstrate that Earth’s climate continues to change.

Scientists have speculated that one of the causes of this plateau in sea-surface temperature could be a change in the exchange of ocean water between warm, surface waters and cold, deep waters below 700 meters, as if the warming is hiding underwater. Temperature measurements at this depth cover a relatively short period. But the warm water won’t hide below the surface forever. Scientists believe it may re-emerge later or affect other climate indicators, such as sea level or ocean circulation.